In the orthodontic art, it is a common practice to place metal, plastic or ceramic brackets upon the teeth in order that an arch wire can be stretched across these brackets for the purpose of properly positioning the teeth. These brackets must have the strength to withstand high pressure when wires are stretched across them. However, the bracket's composition must be susceptible to mechanical (or chemical) bonding to the tooth. Another aspect which must be considered is the aesthetic durability of the bracket.
The original orthodontic brackets were based on metal bands, which were wrapped around the tooth. These were extremely unaesthetic and presented difficulty in the mechanics of moving the tooth into proper position. In addition, these orthodontic appliances were extremely labor intensive and often caused damage to the tooth due to difficulty (or impossibility) of maintaining proper dental hygiene.
A second generation of orthodontic brackets were based on a smaller metal bracket which could be affixed directly to the face of the tooth. These brackets were affixed by mechanical bonding between the etched enamel of the tooth and the interlocking grid structure on the bonding surface of the bracket. While more aesthetic than bands, these metal brackets were still quite unaesthetic. Also, these metal brackets could be difficult to bond to the tooth due to the need to entirely fill the grid structure of the bonding surface of the bracket with adhesive. In addition, these metal brackets were expensive to manufacture due to the complexity of the manufacturing process.
A third generation of orthodontic brackets was the lingual device which was affixed to the back side of the tooth. While this method was more aesthetic than previous ones, it presented difficulties in bonding and practice.
A fourth generation of orthodontic brackets was the plastic bracket. While being moderately aesthetic and inexpensive, these brackets would stain and thereby depreciate the aesthetic quality of the brackets. In addition, the plastic composition did not provide adequate stiffness and often resulted in the plastic bracket detaching from the tooth due to the inability of the bracket to hold the adhesive in place. Also, due to its lack of stiffness, treatment was restricted to cases requiring minimal mechanical treatment.
A fifth generation of orthodontic devices was the ceramic bracket. While this bracket was translucent and thereby very aesthetic, the ceramic composition produced a brittle structure. This bracket was also very abrasive to opposing and impinging teeth as well as the arch wire. In addition, the ceramic bracket was difficult to remove, often resulting in damage to the tooth enamel.
Certain related devices, compositions, and methods are disclosed in U.S. Pat. Nos. 3,895,445; 4,435,160; 4,695,251; and 4,772,325.
Accordingly, it is an object of the present invention to provide a plastic/composite orthodontic bracket which is essentially color neutral and thereby aesthetic due to the transparent (or translucent) properties of the constituents.
It is also an object of the present invention to provide an orthodontic bracket which will not stain, even with exposure to foods and drinks, including coffee, cigarettes, juices, etc.
It is a further object of the invention to provide an orthodontic bracket which is chemically bondable to an etched tooth or enamel surface using standard orthodontic adhesives which are designed to chemically adhere to an etched tooth or enamel surface.
It is a further object of the invention to provide an orthodontic bracket which is stiffer and stronger than other plastic brackets.
It is yet another object of the invention to provide an orthodontic bracket which is both tough with respect to the mechanical stresses and wear of the arch wire dynamics and also non-abrasive when in contact with adjacent and/or impinging teeth.
It is a further object of the invention to provide an orthodontic bracket which is formed by injection or compression molding and is curable by heat, chemical reaction or microwave or other electro-magnetic radiation.
Yet another object of the present invention is to provide an orthodontic bracket which is inexpensive to manufacture.